/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.jmx.support;

import javax.management.MBeanServer;
import javax.management.MBeanServerFactory;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.jmx.MBeanServerNotFoundException;
import org.springframework.lang.Nullable;

/**
 * {@link FactoryBean} that obtains an {@link javax.management.MBeanServer} reference
 * through the standard JMX 1.2 {@link javax.management.MBeanServerFactory}
 * API (which is available on JDK 1.5 or as part of a JMX 1.2 provider).
 * Exposes the {@code MBeanServer} for bean references.
 *
 * <p>By default, {@code MBeanServerFactoryBean} will always create
 * a new {@code MBeanServer} even if one is already running. To have
 * the {@code MBeanServerFactoryBean} attempt to locate a running
 * {@code MBeanServer} first, set the value of the
 * "locateExistingServerIfPossible" property to "true".
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @see #setLocateExistingServerIfPossible
 * @see #locateMBeanServer
 * @see javax.management.MBeanServer
 * @see javax.management.MBeanServerFactory#findMBeanServer
 * @see javax.management.MBeanServerFactory#createMBeanServer
 * @see javax.management.MBeanServerFactory#newMBeanServer
 * @see MBeanServerConnectionFactoryBean
 * @see ConnectorServerFactoryBean
 * @since 1.2
 */
public class MBeanServerFactoryBean implements FactoryBean<MBeanServer>, InitializingBean, DisposableBean {

    protected final Log logger = LogFactory.getLog(getClass());

    private boolean locateExistingServerIfPossible = false;

    @Nullable
    private String agentId;

    @Nullable
    private String defaultDomain;

    private boolean registerWithFactory = true;

    @Nullable
    private MBeanServer server;

    private boolean newlyRegistered = false;


    /**
     * Set whether or not the {@code MBeanServerFactoryBean} should attempt
     * to locate a running {@code MBeanServer} before creating one.
     * <p>Default is {@code false}.
     */
    public void setLocateExistingServerIfPossible(boolean locateExistingServerIfPossible) {
        this.locateExistingServerIfPossible = locateExistingServerIfPossible;
    }

    /**
     * Set the agent id of the {@code MBeanServer} to locate.
     * <p>Default is none. If specified, this will result in an
     * automatic attempt being made to locate the attendant MBeanServer,
     * and (importantly) if said MBeanServer cannot be located no
     * attempt will be made to create a new MBeanServer (and an
     * MBeanServerNotFoundException will be thrown at resolution time).
     * <p>Specifying the empty String indicates the platform MBeanServer.
     *
     * @see javax.management.MBeanServerFactory#findMBeanServer(String)
     */
    public void setAgentId(String agentId) {
        this.agentId = agentId;
    }

    /**
     * Set the default domain to be used by the {@code MBeanServer},
     * to be passed to {@code MBeanServerFactory.createMBeanServer()}
     * or {@code MBeanServerFactory.findMBeanServer()}.
     * <p>Default is none.
     *
     * @see javax.management.MBeanServerFactory#createMBeanServer(String)
     * @see javax.management.MBeanServerFactory#findMBeanServer(String)
     */
    public void setDefaultDomain(String defaultDomain) {
        this.defaultDomain = defaultDomain;
    }

    /**
     * Set whether to register the {@code MBeanServer} with the
     * {@code MBeanServerFactory}, making it available through
     * {@code MBeanServerFactory.findMBeanServer()}.
     *
     * @see javax.management.MBeanServerFactory#createMBeanServer
     * @see javax.management.MBeanServerFactory#findMBeanServer
     */
    public void setRegisterWithFactory(boolean registerWithFactory) {
        this.registerWithFactory = registerWithFactory;
    }


    /**
     * Creates the {@code MBeanServer} instance.
     */
    @Override
    public void afterPropertiesSet() throws MBeanServerNotFoundException {
        // Try to locate existing MBeanServer, if desired.
        if (this.locateExistingServerIfPossible || this.agentId != null) {
            try {
                this.server = locateMBeanServer(this.agentId);
            } catch (MBeanServerNotFoundException ex) {
                // If agentId was specified, we were only supposed to locate that
                // specific MBeanServer; so let's bail if we can't find it.
                if (this.agentId != null) {
                    throw ex;
                }
                logger.info("No existing MBeanServer found - creating new one");
            }
        }

        // Create a new MBeanServer and register it, if desired.
        if (this.server == null) {
            this.server = createMBeanServer(this.defaultDomain, this.registerWithFactory);
            this.newlyRegistered = this.registerWithFactory;
        }
    }

    /**
     * Attempt to locate an existing {@code MBeanServer}.
     * Called if {@code locateExistingServerIfPossible} is set to {@code true}.
     * <p>The default implementation attempts to find an {@code MBeanServer} using
     * a standard lookup. Subclasses may override to add additional location logic.
     *
     * @param agentId the agent identifier of the MBeanServer to retrieve.
     *                If this parameter is {@code null}, all registered MBeanServers are
     *                considered.
     * @return the {@code MBeanServer} if found
     * @throws org.springframework.jmx.MBeanServerNotFoundException if no {@code MBeanServer} could be found
     * @see #setLocateExistingServerIfPossible
     * @see JmxUtils#locateMBeanServer(String)
     * @see javax.management.MBeanServerFactory#findMBeanServer(String)
     */
    protected MBeanServer locateMBeanServer(@Nullable String agentId) throws MBeanServerNotFoundException {
        return JmxUtils.locateMBeanServer(agentId);
    }

    /**
     * Create a new {@code MBeanServer} instance and register it with the
     * {@code MBeanServerFactory}, if desired.
     *
     * @param defaultDomain       the default domain, or {@code null} if none
     * @param registerWithFactory whether to register the {@code MBeanServer}
     *                            with the {@code MBeanServerFactory}
     * @see javax.management.MBeanServerFactory#createMBeanServer
     * @see javax.management.MBeanServerFactory#newMBeanServer
     */
    protected MBeanServer createMBeanServer(@Nullable String defaultDomain, boolean registerWithFactory) {
        if (registerWithFactory) {
            return MBeanServerFactory.createMBeanServer(defaultDomain);
        } else {
            return MBeanServerFactory.newMBeanServer(defaultDomain);
        }
    }


    @Override
    @Nullable
    public MBeanServer getObject() {
        return this.server;
    }

    @Override
    public Class<? extends MBeanServer> getObjectType() {
        return (this.server != null ? this.server.getClass() : MBeanServer.class);
    }

    @Override
    public boolean isSingleton() {
        return true;
    }


    /**
     * Unregisters the {@code MBeanServer} instance, if necessary.
     */
    @Override
    public void destroy() {
        if (this.newlyRegistered) {
            MBeanServerFactory.releaseMBeanServer(this.server);
        }
    }

}
